Two-part, cyanoacrylate/free radically curable adhesive systems

ABSTRACT

Two-part cyanoacrylate/free radically curable adhesive systems demonstrating improved toughness are provided.

BACKGROUND Field

Two-part cyanoacrylate/free radically curable adhesive systemsdemonstrating improved toughness are provided.

Brief Discussion of Related Technology

Curable compositions such as cyanoacrylate adhesives are well recognizedfor their excellent ability to rapidly bond a wide range of substrates,generally in a number of minutes and depending on the particularsubstrate, often in a number of seconds.

Polymerization of cyanoacrylates is initiated by nucleophiles foundunder normal atmospheric conditions on most surfaces. The initiation bysurface chemistry means that sufficient initiating species are availablewhen two surfaces are in close contact with a small layer ofcyanoacrylate between the two surfaces. Under these conditions a strongbond is obtained in a short period of time. Thus, in essence thecyanoacrylate often functions as an instant adhesive.

Cyanoacrylate adhesive performance, particularly durability, oftentimesbecomes suspect when exposed to elevated temperature conditions and/orhigh relative humidity conditions. To combat these application-dependentshortcomings, a host of additives have been identified for inclusion incyanoacrylate adhesive formulations. Improvements would still be seen asbeneficial.

A variety of additives and fillers have been added to cyanoacrylatecompositions to modify physical properties.

For instance, U.S. Pat. No. 3,183,217 to Serniuk et al. discloses freeradical polymerization of a methacrylic acid or methyl methacrylatemonomer with a non-polar or mildly polar olefin where the monomer iscomplexed with a Friedel-Crafts halide.

U.S. Pat. No. 3,963,772 to Takeshita discloses liquid telomers ofalkylene and acrylic monomers which result in short chain alternatingcopolymers substantially terminated at one end of the polymer chainswith the more reactive alkylene units. The liquid telomers are useful inmaking elastomeric polymers for high molecular weight rubbers whichpermit the ready incorporation of fillers, additives, and the like, dueto its liquid phase.

U.S. Pat. No. 4,440,910 to O'Connor is directed to cyanoacrylatecompositions having improved toughness, achieved through the addition ofelastomers, i.e., acrylic rubbers. These rubbers are either (i)homopolymers of alkyl esters of acrylic acid; (ii) copolymers of anotherpolymerizable monomer, such as lower alkenes, with an alkyl ester ofacrylic acid or with an alkoxy ester of acrylic acid; (iii) copolymersof alkyl esters of acrylic acid; (iv) copolymers of alkoxy esters ofacrylic acid; and (v) mixtures thereof.

U.S. Pat. No. 4,560,723 to Millet et al. discloses a cyanoacrylateadhesive composition containing a toughening agent comprising acore-shell polymer and a sustainer comprising an organic compoundcontaining one or more unsubstituted or substituted aryl groups. Thesustainer is reported to improve retention of toughness after heat agingof cured bonds of the adhesive. The core-shell polymer is treated withan acid wash to remove any polymerization-causing impurities such assalts, soaps or other nucleophilic species left over from the core-shellpolymer manufacturing process.

U.S. Pat. No. 5,340,873 to Mitry discloses a cyanoacrylate adhesivecomposition having improved toughness by including an effectivetoughening amount of a polyester polymer derived from a dibasicaliphatic or aromatic carboxylic acid and a glycol.

U.S. Pat. No. 5,994,464 to Ohsawa et al. discloses a cyanoacrylateadhesive composition containing a cyanoacrylate monomer, an elastomermiscible or compatible with the cyanoacrylate monomer, and a core-shellpolymer being compatible, but not miscible, with the cyanoacrylatemonomer.

U.S. Pat. No. 6,833,196 to Wojciak discloses a method of enhancing thetoughness of a cyanoacrylate composition between steel and EPDM rubbersubstrates. The disclosed method is defined by the steps of: providing acyanoacrylate component; and providing a toughening agent comprisingmethyl methacrylic monomer and at least one of butyl acrylic monomer andisobornyl acrylic monomer, whereby the acrylic monomer toughening agentenhances the toughness of the cyanoacrylate composition such thatwhereupon cure, the cyanoacrylate composition has an average tensileshear strength of over about 4400 psi after 72 hours at room temperaturecure and 2 hours post cure at 121° C.

Reactive acrylic adhesives that cure by free radical polymerization of(meth)acrylic esters (i.e., acrylates) are known, but suffer fromcertain drawbacks. Commercially important acrylic adhesives tend to havean offensive odor, particularly those that are made from methylmethacrylate. Methyl methacrylate-based acrylic adhesives also have lowflash points (approximately 59° F.). Low flash points are particularlyan issue during storage and transportation of the adhesives. If theflash point is 141° F. or lower, the U.S. Department of Transportationclassifies the product as “Flammable” and requires marking and specialstorage and transportation conditions.

U.S. Pat. No. 6,562,181 to Righettini intended to provide a solution tothe problem addressed in the preceding paragraph by describing anadhesive composition comprising: (a) a trifunctional olefinic firstmonomer comprising an olefinic group that has at least three functionalgroups each bonded directly to the unsaturated carbon atoms of saidolefinic group; (b) an olefinic second monomer that is copolymerizablewith the first monomer; (c) a redox initiator system, and (d) a reactivediluent, where the composition is a liquid at room temperature is 100%reactive and substantially free of volatile organic solvent, and iscurable at room temperature.

And more recently, U.S. Pat. No. 9,371,470 to Burns described andclaimed a two-part curable composition comprising: (a) a first partcomprising a cyanoacrylate component and a peroxide catalyst; and (b) asecond part comprising a free radical curable component and a transitionmetal. When mixed together the peroxide catalyst initiates cure of thefree radical curable component and the transition metal initiates cureof the cyanoacrylate component. In a particular embodiment, the peroxidecatalyst is t-butyl perbenzoate.

Notwithstanding the state of the art, it would be desirable to providean adhesive system having both the features of an instant adhesive, suchas in terms of the fast fixture times and ability to bond a wide rangeof substrates such as metals and plastics observed with cyanoacrylates,together with the improved bond strength over a greater variety and/orselection of substrates seen with (meth)acrylate compositions. And itwould be desirable to provide a two-part reactive adhesive with reducedodor and flammability that could be mixed at a 1:1 volume ratio withoutcomprising shelf life stability or adhesive performance. In addition, itwould be desirable for the two-part reactive adhesive to be toughened sothat reaction products thereof can withstand exposure to a variety ofextreme conditions without sacrificing useful bond strength.

SUMMARY

There is provided in one aspect a two-part cyanoacrylate/free radicallycurable composition comprising:

-   -   (a) a first part comprising a cyanoacrylate component and a        peroxide catalyst; and    -   (b) a second part comprising a free radical curable component        and a transition metal.        When mixed together, the peroxide catalyst of the first part        initiates cure of the free radically curable component of the        second part and the transition metal of the second part        initiates cure of the cyanoacrylate of the first part.

Significantly, in at least one of the first part or the second part isfurther provided a (meth)acrylate-functionalized compound having a Tgless than 0, such as less than 0 to about −120° C.

The compositions, which are room temperature curable as the first partand the second part do not interact prior to use on mixing, provide goodperformance across substrates constructed from a wide variety ofmaterials and provide improved durability performance over conventionalcyanoacrylate compositions and improved fixture time and improved bondstrength over conventional free radical curable compositions.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1-2 depict bar charts of various adhesive systems used to bondmetal (i.e., grit blasted mild steel and aluminum) substrates shown onthe X axis and impact toughness performance measured at 0 gap and 1 mmgap in Joules shown on the Y axis.

DETAILED DESCRIPTION Part A

The cyanoacrylate component includes cyanoacrylate monomers, such asthose represented by H₂C═C(CN)—COOR, where R is selected from C₁₋₁₅alkyl, C₂₋₁₅ alkoxyalkyl, C₃₋₁₅ cycloalkyl, C₂₋₁₅ alkenyl, C₇₋₁₅aralkyl, C₆₋₁₅ aryl, C₃₋₁₅ allyl and C₁₋₁₅ haloalkyl groups. Desirably,the cyanoacrylate monomer is selected from methyl cyanoacrylate,ethyl-2-cyanoacrylate (“ECA”), propyl cyanoacrylates, butylcyanoacrylates (such as n-butyl-2-cyanoacrylate), octyl cyanoacrylates,allyl cyanoacrylate, B methoxyethyl cyanoacrylate and combinationsthereof. A particularly desirable one is ethyl-2-cyanoacrylate.

The cyanoacrylate component should be included in the Part A compositionin an amount within the range of from about 50 percent by weight toabout 99.98 percent by weight, such as about 90 percent by weight toabout 99 percent by weight being desirable, and about 92 percent byweight to about 97 percent by weight of the Part A composition beingparticularly desirable.

As the peroxide catalyst to be included in the Part A composition of thetwo-part adhesive system, perbenzoates should be used, such ast-butylperbenzoate.

Typically, the amount of peroxide catalyst should fall in the range ofabout 0.001 percent by weight up to about 10.00 percent by weight of thecomposition, desirably about 0.01 percent by weight up to about 5.00percent by weight of the composition, such as about 0.50 to 2.50 percentby weight of the composition.

Additives may be included in the Part A composition of the adhesivesystem to modify physical properties, such as improved fixture speed,improved shelf-life stability, flexibility, thixotropy, increasedviscosity, color, and improved toughness. Such additives therefore maybe selected from accelerators, free radical stabilizers, anionicstabilizers, gelling agents, thickeners [such as PMMAs], thixotropyconferring agents (such as fumed silica), dyes, toughening agents,plasticizers and combinations thereof.

The toughening agent used in the Part A composition are those that havebeen found to be compatible with cyanoacrylate.

One or more accelerators may also be used in the adhesive system,particularly, in the Part A composition, to accelerate cure of thecyanoacrylate component. Such accelerators may be selected fromcalixarenes and oxacalixarenes, silacrowns, crown ethers, cyclodextrins,poly(ethyleneglycol) di(meth)acrylates, ethoxylated hydric compounds andcombinations thereof.

Of the calixarenes and oxacalixarenes, many are known, and are reportedin the patent literature. See e.g. U.S. Pat. Nos. 4,556,700, 4,622,414,4,636,539, 4,695,615, 4,718,966, and 4,855,461, the disclosures of eachof which are hereby expressly incorporated herein by reference.

For instance, as regards calixarenes, those within the structure beloware useful herein:

where R¹ is alkyl, alkoxy, substituted alkyl or substituted alkoxy; R²is H or alkyl; and n is 4, 6 or 8.

One particularly desirable calixarene is tetrabutyltetra[2-ethoxy-2-oxoethoxy]calix-4-arene.

A host of crown ethers are known. For instance, examples which may beused herein either individually or in combination include 15-crown-5,18-crown-6, dibenzo-18-crown-6, benzo-15-crown-5-dibenzo-24-crown-8,dibenzo-30-crown-10, tribenzo-18-crown-6, asym-dibenzo-22-crown-6,dibenzo-14-crown-4, dicyclohexyl-18-crown-6, dicyclohexyl-24-crown-8,cyclohexyl-12-crown-4, 1,2-decalyl-15-crown-5, 1,2-naphtho-15-crown-5,3,4,5-naphtyl-16-crown-5, 1,2-methyl-benzo-18-crown-6,1,2-methylbenzo-5, 6-methylbenzo-18-crown-6, 1,2-t-butyl-18-crown-6,1,2-vinylbenzo-15-crown-5, 1,2-vinylbenzo-18-crown-6,1,2-t-butyl-cyclohexyl-18-crown-6, asym-dibenzo-22-crown-6 and1,2-benzo-1,4-benzo-5-oxygen-20-crown-7. See U.S. Pat. No. 4,837,260(Sato), the disclosure of which is hereby expressly incorporated here byreference.

Of the silacrowns, again many are known, and are reported in theliterature. For instance, a typical silacrown may be represented withinthe structure below:

where R³ and R⁴ are organo groups which do not themselves causepolymerization of the cyanoacrylate monomer, R⁵ is H or CH₃ and n is aninteger of between 1 and 4. Examples of suitable R³ and R⁴ groups are Rgroups, alkoxy groups, such as methoxy, and aryloxy groups, such asphenoxy. The R³ and R⁴ groups may contain halogen or other substituents,an example being trifluoropropyl. However, groups not suitable as R⁴ andR⁵ groups are basic groups, such as amino, substituted amino andalkylamino.

Specific examples of silacrown compounds useful in the inventivecompositions include:

dimethylsila-11-crown-4;

dimethylsila-14-crown-5;

and dimethylsila-17-crown-6. See e.g. U.S. Pat. No. 4,906,317 (Liu), thedisclosure of which is hereby expressly incorporated herein byreference.

Many cyclodextrins may be used in connection with the present invention.For instance, those described and claimed in U.S. Pat. No. 5,312,864(Wenz), the disclosure of which is hereby expressly incorporated hereinby reference, as hydroxyl group derivatives of an α, β or γ-cyclodextrinwhich is at least partly soluble in the cyanoacrylate would beappropriate choices for use herein as an accelerator component.

In addition, poly(ethylene glycol) di(meth)acrylates suitable for useherein include those within the structure below:

where n is greater than 3, such as within the range of 3 to 12, with nbeing 9 as particularly desirable. More specific examples include PEG200 DMA (where n is about 4), PEG 400 DMA (where n is about 9), PEG 600DMA (where n is about 14), and PEG 800 DMA (where n is about 19), wherethe number (e.g., 400) represents the average molecular weight of theglycol portion of the molecule, excluding the two methacrylate groups,expressed as grams/mole (i.e., 400 g/mol). A particularly desirable PEGDMA is PEG 400 DMA.

And of the ethoxylated hydric compounds (or ethoxylated fatty alcoholsthat may be employed), appropriate ones may be chosen from those withinthe structure below:

where C_(m) can be a linear or branched alkyl or alkenyl chain, m is aninteger between 1 to 30, such as from 5 to 20, n is an integer between 2to 30, such as from 5 to 15, and R may be H or alkyl, such as C₁₋₆alkyl.

In addition, accelerators embraced within the structure below:

where R is hydrogen, C₁₋₆ alkyl, C₁₋₆ alkyloxy, alkyl thioethers,haloalkyl, carboxylic acid and esters thereof, sulfinic, sulfonic andsulfurous acids and esters, phosphinic, phosphonic and phosphorous acidsand esters thereof, Z is a polyether linkage, n is 1-12 and p is 1-3 areas defined above, and R′ is the same as R, and g is the same as n.

A particularly desirable chemical within this class as an acceleratorcomponent is

where n and m combined are greater than or equal to 12.

The accelerator should be included in the composition in an amountwithin the range of from about 0.01 percent by weight to about 10percent by weight, with the range of about 0.1 to about 0.5 percent byweight being desirable, and about 0.4 percent by weight of the totalcomposition being particularly desirable.

Stabilizers useful in the Part A composition of the adhesive systeminclude free-radical stabilizers, anionic stabilizers and stabilizerpackages that include combinations thereof. The identity and amount ofsuch stabilizers are well known to those of ordinary skill in the art.See e.g. U.S. Pat. Nos. 5,530,037 and 6,607,632, the disclosures of eachof which are hereby incorporated herein by reference. Commonly usedfree-radical stabilizers include hydroquinone, while commonly usedanionic stabilizers include boron triflouride, borontrifluoride-etherate, sulphur trioxide (and hydrolyis products thereof)and methane sulfonic acid.

Part B

Free radical curable monomers for use in the Part B composition of theadhesive system include (meth)acrylate monomers, maleimide-,itaconamide- or nadimide-containing compounds and combinations thereof.

(Meth)acrylate monomers for use in Part B of the composition of theadhesive system include a host of (meth)acrylate monomers, with some ofthe (meth)acrylate monomers being aromatic, while others are aliphaticand still others are cycloaliphatic. Examples of such (meth)acrylatemonomers include di-or tri-functional (meth)acrylates like polyethyleneglycol di(meth)acrylates, tetrahydrofuran (meth)acrylates anddi(meth)acrylates, hydroxypropyl (meth)acrylate (“HPMA”), hexanedioldi(meth)acrylate, trimethylol propane tri(meth)acrylate (“TMPTMA”),diethylene glycol dimethacrylate, triethylene glycol dimethacrylate(“TRIEGMA”), benzylmethacrylate, tetraethylene glycol dimethacrylate,dipropylene glycol dimethacrylate, di-(pentamethylene glycol)dimethacrylate, tetraethylene diglycol diacrylate, diglyceroltetramethacrylate, tetramethylene dimethacrylate, ethylenedimethacrylate, neopentyl glycol diacrylate, trimethylol propanetriacrylate and bisphenol-A mono and di(meth)acrylates, such asethoxylated bisphenol-A (meth)acrylate (“EBIPMA”), bisphenol-F mono anddi(meth)acrylates, such as ethoxylated bisphenol-F (meth)acrylate, and(meth)acrylate-functionalized urethanes.

For instance, examples of such (meth)acrylate-functionalized urethanesinclude a tetramethylene glycol urethane acrylate oligomer and apropylene glycol urethane acrylate oligomer.

Other (meth)acrylate-functionalized urethanes are urethane(meth)acrylate oligomers based on polyethers or polyesters, which arereacted with aromatic, aliphatic, or cycloaliphatic diisocyanates andcapped with hydroxy acrylates. For instance, difunctional urethaneacrylate oligomers, such as a polyester of hexanedioic acid anddiethylene glycol, terminated with isophorone diisocyanate, capped with2-hydroxyethyl acrylate (CAS 72121-94-9); a polypropylene glycolterminated with tolyene-2,6-diisocyanate, capped with2-hydroxyethylacrylate (CAS 37302-70-8); a polyester of hexanedioic acidand diethylene glycol, terminated with 4,4′-methylenebis(cyclohexylisocyanate), capped with 2-hydroxyethyl acrylate (CAS 69011-33-2); apolyester of hexanedioic acid, 1,2-ethanediol, and 1,2 propanediol,terminated with tolylene-2,4-diisocyanate, capped with 2-hydroxyethylacrylate (CAS 69011-31-0); a polyester of hexanedioic acid,1,2-ethanediol, and 1,2 propanediol, terminated with4,4′-methylenebis(cyclohexyl isocyanate, capped with 2-hydroxyethylacrylate (CAS 69011-32-1); and a polytetramethylene glycol etherterminated with 4,4′-methylenebis(cyclohexylisocyanate), capped with2-hydroxyethyl acrylate.

Still other (meth)acrylate-functionalized urethanes are monofunctionalurethane acrylate oligomers, such as a polypropylene terminated with4,4′-methylenebis(cyclohexylisocyanate), capped with 2-hydroxyethylacrylate and 1-dodosanol.

They also include difunctional urethane methacrylate oligomers such as apolytetramethylene glycol ether terminated withtolulene-2,4-diisocyanate, capped with 2-hydroxyethyl methacrylate; apolytetramethylene glycol ether terminated with isophorone diisocyanate,capped with 2-hydroxyethyl methacrylate; a polytetramethylene glycolether terminated with 4,4′-methylenebis(cyclohexylisocyanate), cappedwith 2-hydroxyethyl methacrylate; and a polypropylene glycol terminatedwith tolylene-2,4-diisocyanate, capped with 2-hydroxyethyl methacrylate.

The maleimides, nadimides, and itaconimides include those compoundshaving the following structures I, II and III, respectively

where:

-   -   m=1-15,    -   p=0-15,        -   each R² is independently selected from hydrogen or lower            alkyl, and        -   J is a monovalent or a polyvalent moiety comprising organic            or organosiloxane radicals, and combinations of two or more            thereof.

More specific representations of the maleimides, itaconimides andnadimides include those corresponding to structures I, II, or III, wherem=1-6, p=0, R² is independently selected from hydrogen or lower alkyl,and J is a monovalent or polyvalent radical selected from hydrocarbyl,substituted hydrocarbyl, heteroatom-containing hydrocarbyl, substitutedheteroatom-containing hydrocarbyl, hydrocarbylene, substitutedhydrocarbylene, heteroatom-containing hydrocarbylene, substitutedheteroatom-containing hydrocarbylene, polysiloxane,polysiloxane-polyurethane block copolymer, and combinations of two ormore thereof, optionally containing one or more linkers selected from acovalent bond, —O—, —S—, —NR—, —O—C(O)—, —O—C(O)—O—, —O—C(O)—NR—,—NR—C(O)—, —NR—C(O)—O—, —NR—C(O)—NR—, —S—C(O)—, —S—C(O)—O—, —S—C(O)—NR—,—S(O)—, —S(O)₂—, —O—S(O)₂—, —O—S(O)₂—O—, —O—S(O)₂—NR—, —O—S(O)—,—O—S(O)—O—, —O—S(O)—NR—, —O—NR—C(O)—, —O—NR—C(O)—O—, —O—NR—C(O)—NR—,—NR—O—C(O)—, —NR—O—C(O)—O—, —NR—O—C(O)—NR—, —O—NR—C(S)—, —O—NR—C(S)—O—,—O—NR—C(S)—NR—, —NR—O—C(S)—, —NR—O—C(S)—O—, —NR—O—C(S)—NR—, —O—C(S)—,—O—C(S)—O—, —O—C(S)—NR—, —NR—C(S)—, —NR—C(S)—O—, —NR—C(S)—NR—,—S—S(O)₂—, —S—S(O)₂—O—, —S—S(O)₂—NR—, —NR—O—S(O)—, —NR—O—S(O)—O—,—NR—O—S(O)—NR—, —NR—O—S(O)₂—, —NR—O—S(O)₂—O—, —NR—O—S(O)₂—NR—,—O—NR—S(O)—, —O—NR—S(O)—O—, —O—NR—S(O)—NR—, —O—NR—S(O)₂—O—,—O—NR—S(O)₂—NR—, —O—NR—S(O)₂—, —O—P(O)R₂—, —S—P(O)R₂—, —NR—P(O)R₂—,where each R is independently hydrogen, alkyl or substituted alkyl, andcombinations of any two or more thereof.

When one or more of the above described monovalent or polyvalent groupscontain one or more of the above described linkers to form the “J”appendage of a maleimide, a nadimide or an itaconimide group, as readilyrecognized by those of skill in the art, a wide variety of linkers canbe produced, such as, for example, oxyalkyl, thioalkyl, aminoalkyl,carboxylalkyl, oxyalkenyl, thioalkenyl, aminoalkenyl, carboxyalkenyl,oxyalkynyl, thioalkynyl, aminoalkynyl, carboxyalkynyl, oxycycloalkyl,thiocycloalkyl, aminocycloalkyl, carboxycycloalkyl, oxycloalkenyl,thiocycloalkenyl, aminocycloalkenyl, carboxycycloalkenyl, heterocyclic,oxyheterocyclic, thioheterocyclic, aminoheterocyclic,carboxyheterocyclic, oxyaryl, thioaryl, aminoaryl, carboxyaryl,heteroaryl, oxyheteroaryl, thioheteroaryl, aminoheteroaryl,carboxyheteroaryl, oxyalkylaryl, thioalkylaryl, aminoalkylaryl,carboxyalkylaryl, oxyarylalkyl, thioarylalkyl, aminoarylalkyl,carboxyarylalkyl, oxyarylalkenyl, thioarylalkenyl, aminoarylalkenyl,carboxyarylalkenyl, oxyalkenylaryl, thioalkenylaryl, aminoalkenylaryl,carboxyalkenylaryl, oxyarylalkynyl, thioarylalkynyl, aminoarylalkynyl,carboxyarylalkynyl, oxyalkynylaryl, thioalkynylaryl, aminoalkynylaryl orcarboxyalkynylaryl, oxyalkylene, thioalkylene, aminoalkylene,carboxyalkylene, oxyalkenylene, thioalkenylene, aminoalkenylene,carboxyalkenylene, oxyalkynylene, thioalkynylene, aminoalkynylene,carboxyalkynylene, oxycycloalkylene, thiocycloalkylene,aminocycloalkylene, carboxycycloalkylene, oxycycloalkenylene,thiocycloalkenyle aminoalkylarylene, carboxyalkylarylene,oxyarylalkylene, thioarylalkylene, aminoarylalkylene,carboxyarylalkylene, oxyarylalkenylene, thioarylalkenylene,aminoarylalkenylene, carboxyarylalkenylene, oxyalkenylarylene,thioalkenylarylene, aminoalkenylarylene, carboxyalkenylarylene,oxyarylalkynylene, thioarylalkynylene, aminoarylalkynylene, carboxyarylalkynylene, oxyalkynylarylene, thioalkynylarylene,aminoalkynylarylene, carboxyalkynylarylene, heteroarylene,oxyheteroarylene, thioheteroarylene, aminoheteroarylene,carboxyheteroarylene, heteroatom-containing di- or polyvalent cyclicmoiety, oxyheteroatom-containing di- or polyvalent cyclic moiety,thioheteroatom-containing di- or polyvalent cyclic moiety,aminoheteroatom-containing di- or polyvalent cyclic moiety,carboxyheteroatom-containing di- or polyvalent cyclic moiety, disulfide,sulfonamide, and the like. ne, aminocycloalkenylene,carboxycycloalkenylene, oxyarylene, thioarylene, aminoarylene,carboxyarylene, oxyalkylarylene, thioalkylarylene,

In another embodiment, maleimides, nadimides, and itaconimidescontemplated for use in the practice of the present invention have thestructures I, II, and III, where m=1-6, p=0-6, and J is selected fromsaturated straight chain alkyl or branched chain alkyl, optionallycontaining optionally substituted aryl moieties as substituents on thealkyl chain or as part of the backbone of the alkyl chain, and where thealkyl chains have up to about 20 carbon atoms;

a siloxane having the structure:—(C(R³)₂)_(d)—[Si(R⁴)₂—O]_(f)—Si(R⁴)₂—(C(R³)₂)_(e)—,—(C(R³)₂)_(d)—C(R³)—C(O)O—(C(R³)₂)_(d)—[Si(R⁴)₂—O]_(f)—Si(R⁴)₂—(C(R³)₂)_(e)—O(O)C—(C(R³)₂)_(e)—,or—(C(R³)₂)_(d)—C(R³)—O(O)C—(C(R³)₂)_(d)—[Si(R⁴)₂—O]_(f)—Si(R⁴)₂—(C(R³)₂)_(e)—C(O)O— (C(R³)₂)_(e)—, where:

each R³ is independently hydrogen, alkyl or substituted alkyl,

each R⁴ is independently hydrogen, lower alkyl or aryl,

d=1-10,

e=1-10, and

f=1-50;

a polyalkylene oxide having the structure:

[(CR₂)_(f)—O—]_(f)—(CR₂)_(s)—

where:

each R is independently hydrogen, alkyl or substituted alkyl,

r=1-10,

s=1-10, and

f is as defined above;

aromatic groups having the structure:

where:

each Ar is a monosubstituted, disubstituted or trisubstituted aromaticor heteroaromatic ring having in the range of 3 up to 10 carbon atoms,and

Z is:

-   -   saturated straight chain alkylene or branched chain alkylene,        optionally containing saturated cyclic moieties as substituents        on the alkylene chain or as part of the backbone of the alkylene        chain, or polyalkylene oxides having the structure:

[(CR₂)_(r)—O—]_(q)—(CR₂)_(s)—

where:

-   -   each R is independently hydrogen, alkyl or substituted alkyl, r        and s are each defined as above, and    -   q falls in the range of 1 up to 50;    -   di- or tri-substituted aromatic moieties having the structure:

where:

each R is independently hydrogen, alkyl or substituted alkyl,

t falls in the range of 2 up to 10,

u falls in the range of 2 up to 10, and

Ar is as defined above;

-   -   aromatic groups having the structure:

where:

each R is independently hydrogen, alkyl or substituted alkyl,

t=2-10,

k=1, 2 or 3,

g=1 up to about 50,

each Ar is as defined above,

E is —O— or —NR⁵—, where R⁵ is hydrogen or lower alkyl; and

W is straight or branched chain alkyl, alkylene, oxyalkylene, alkenyl,alkenylene, oxyalkenylene, ester, or polyester, a siloxane having thestructure —(C(R³)₂)_(d)—[Si(R⁴)₂—O]_(f)—Si(R⁴)₂—(C(R³)₂)_(e)—,(R³)₂)_(d)—C(R³)—C(O)O—(C(R³)₂)_(d)—[Si(R⁴)₂—O]_(f)—Si(R⁴)₂—(C(R³)₂)_(e)—O(O)C—(C(R³)₂)_(e)—, or(C(R³)₂)_(d)—C(R³)—O(O)C—(C(R³)₂)_(d)—[Si(R⁴)₂—O]_(f)—Si(R⁴)₂—(C(R³)₂)_(e)—C(O)(C(R³)₂)_(e)—, where:

-   -   each R³ is independently hydrogen, alkyl or substituted alkyl,    -   each R⁴ is independently hydrogen, lower alkyl or aryl,    -   d=1-10,    -   e=1-10, and    -   f=1-50;    -   a polyalkylene oxide having the structure:

[(CR₂)_(f)—O—]_(f)—(CR₂)_(s)—

where:

each R is independently hydrogen, alkyl or substituted alkyl,

r=1-10,

s=1-10, and

f is as defined above;

optionally containing substituents selected from hydroxy, alkoxy,carboxy, nitrile, cycloalkyl or cycloalkenyl;

a urethane group having the structure:

R⁷—U—C(O)—NR⁶—R⁸—NR⁶—C(O)—(O—R⁸—O—C(O)—NR⁶—R⁸—NR⁶—C(O))_(v)—U—R⁸—

where:

each R⁶ is independently hydrogen or lower alkyl,

each R⁷ is independently an alkyl, aryl, or arylalkyl group having 1 to18 carbon atoms,

each R⁸ is an alkyl or alkyloxy chain having up to about 100 atoms inthe chain, optionally substituted with Ar,

U is —O—, —S—, —N(R)—, or —P(L)_(1,2)—,

where R as defined above, and where each L is independently ═O, ═S,—OR—R; and

v=0-50;

-   -   polycyclic alkenyl; or mixtures of any two or more thereof.

In a more specific recitation of such maleimide-, nadimide-, anditaconimide-containing compounds of structures I, II and III,respectively, each R is independently hydrogen or lower alkyl (such asC₁₋₄), -J- comprises a branched chain alkyl, alkylene, alkylene oxide,alkylene carboxyl or alkylene amido species having sufficient length andbranching to render the maleimide, nadimide and/or itaconimide compounda liquid, and m is 1, 2 or 3.

Particularly desirable maleimide-containing compounds include those havetwo maleimide groups with an aromatic group therebetween, such as aphenyl, biphenyl, bisphenyl or napthyl linkage.

In addition to the free radical curable component, Part B also includesa transition metal compound. A non-exhaustive list of representativeexamples of the transition metal compounds are copper, vanadium, cobaltand iron compounds. For instance, as regards copper compounds, coppercompounds where copper enjoys a 1+ or 2+ valence state are desirable. Anon-exhaustive list of examples of such copper (I) and (II) compoundsinclude copper (II) 3,5-diisopropylsalicylate hydrate, copperbis(2,2,6,6-tetramethyl-3,5-heptanedionate), copper (II) hydroxidephosphate, copper (II) chloride, copper (II) acetate monohydrate,tetrakis(acetonitrile)copper (I) hexafluorophosphate, copper (II)formate hydrate, tetrakisacetonitrile copper (I) triflate,copper(II)tetrafluoroborate, copper (II) perchlorate,tetrakis(acetonitrile)copper (I) tetrafluoroborate, copper (II)hydroxide, copper (II) hexafluoroacetylacetonate hydrate and copper (II)carbonate. These copper (I) and (II) compounds should be used in anamount such that when dissolved or suspended in a carrier vehicle, suchas a (meth)acrylate, a concentration of about 100 ppm to about 5,000ppm, such as about 500 ppm to about 2,500 ppm, for instance about 1,000ppm is present in the solution or suspension.

As regards vanadium compounds, vanadium compounds where vanadium enjoysa 2+ and 3+ valence state are desirable. Examples of such vanadium (III)compounds include vanadyl naphthanate and vanadyl acetylacetonate. Thesevanadium (III) compounds should be used in an amount of 50 ppm to about5,000 ppm, such as about 500 ppm to about 2,500 ppm, for instance about1,000 ppm.

As regards cobalt compounds, cobalt compounds where cobalt enjoys a 2+valence state are desirable. Examples of such cobalt (II) compoundsinclude cobalt naphthenate, cobalt tetrafluoroborate and cobaltacetylacetonate. These cobalt (II) compounds should be used in an amountof about 100 ppm to about 1000 ppm.

As regards iron compounds, iron compounds where iron enjoys a 3+ valencestate are desirable. Examples of such iron (III) compounds include ironacetate, iron acetylacetonate, iron tetrafluoroborate, iron perchlorate,and iron chloride. These iron compounds should be used in an amount ofabout 100 ppm to about 1000 ppm.

Also included in at least one of the Part A or the Part B compositionsis a (meth)acrylate-functionalized compound having a Tg of less than 0.Desirably, the (meth)acrylate functionalized monomer should have a Tg inthe range of less than 0 to about −120° C., such as about −5 to about−78° C. Tg here is determined by Dynamic Mechanical Analysis (“DMA”) andis measured in ° C., whether noted or not.

Examples of such (meth)acrylate functionalized monomers include avariety of monomers available commercially from Sartomer Inc., Exton,Pa., now part of the Arkema Group. Particularly desirable (meth)acrylatefunctionalized monomers having a Tg of less than 0 include SR-256(2(2-ethoxyethoxv)-ethyl acrylate, 54° C.), SR-335 (lauryl acrylate,−30° C.), and SR-278 (monofunctional acrylate ester, −78° C.).Additional examples include CD-9075 (alkoxylated lauryl acrylate, alsofrom Sartomer, −45° C.) and polypropylene glycol diacrylate.

Also embraced by such (meth)acrylate functionalized monomers are(meth)acrylate-functionalized urethane resins made with an isophoranediisocyanate may be used. For instance, a polyester of hexanedioic acid,diethylene glycol, terminated with isophorone diisocyanate, capped with2-hydroxyethyl acrylate (CAS 72121-94-9) and a hydroxy terminatedpolybutadiene terminated with isophorone diisocyanate, capped with2-hydroxyethyl acrylate are appropriate examples, as the Tg of suchresins is below 0° C.

In addition, some of these (meth)acrylate-functionalized urethane resinsmay be commercially available. Examples of commercially available resinsinclude those from Dymax Corporation, such as BR-345 (promoted by Dymaxin its 2018 “BOMAR Oligomers Selected Guide,” page 12 as a polyetherurethane acrylate with a Tg by DMA of −57° C.). Other(meth)acrylate-functionalized urethane resins commercially availablefrom Dymax include the polyester urethane acrylates, BR-744BT (−18° C.)and BR-7432 GB (−60° C.); the polyether urethane acrylates, BR-343 (−43°C.), BR-344 (−48° C.), BR-345 (−57° C.), BR-374 (−48° C.), BR-543 (−52°C.), BR-3042 (−37° C.), BR-3641AJ (−50° C.), BR-3741 (−51° C.),BR-3741AJ (−50° C.), BR-744BT (−18° C.), and BR-7432 GB (−60° C.); thepolyether urethane methacrylates, BR-116 (−18° C.), BR-204 (−43° C.),and BR-543 MB (−56° C.). With respect to at least BR-345, see also A.Prabhakar et al., “Structural Investigations of Polypropylene glycol(PPG) and Isophorone diisocyanate (IPDI)-based Polyurethane glycol by 1Dand 21D NMR. Spectroscopy”, J. Polym. Sci.: Part A. Polym. Chem., 43,1196-1209 (2005).

BR-345 may be considered made according to the following reactionscheme:

The amount of the (meth)acrylate-functionalized compound having a Tg ofless than 0 may range from about 5 percent by weight to about 50 percentby weight, such as about 15 percent by weight to about 35 percent byweight, desirably about 25 to about 30 percent by weight.

As discussed above, additives may be included in either or both of thePart A or the Part B compositions to influence a variety of performanceproperties.

Fillers contemplated for use include, for example, aluminum nitride,boron nitride, silicon carbide, diamond, graphite, beryllium oxide,magnesia, silicas, such as fumed silica or fused silica, alumina,perfluorinated hydrocarbon polymers (i.e., TEFLON), thermoplasticpolymers, thermoplastic elastomers, mica, glass powder and the like.Preferably, the particle size of these fillers will be about 20 micronsor less.

As regards silicas, the silica may have a mean particle diameter on thenanoparticle size; that is, having a mean particle diameter on the orderof 10⁻⁹ meters. The silica nanoparticles can be pre-dispersed in epoxyresins, and may be selected from those available under the tradenameNANOPOCRYL, from Nanoresins, Germany. NANOCRYL is a tradename for aproduct family of silica nanoparticle reinforced (meth)acrylates. Thesilica phase consists of surface-modified, synthetic SiO₂ nanosphereswith less than 50 nm diameter and an extremely narrow particle sizedistribution. The SiO₂ nanospheres are agglomerate-free dispersions inthe (meth)acrylate matrix resulting in a low viscosity for resinscontaining up to 50 percent by weight silica.

The silica component should be present in an amount in the range ofabout 1 to about 60 percent by weight, such as about 3 to about 30percent by weight, desirably about 5 to about 20 percent by weight,based on the total weight of the composition.

Tougheners contemplated for use particularly in the Part A compositioninclude elastomeric polymers selected from elastomeric copolymers of alower alkene monomer and (i) acrylic acid esters, (ii) methacrylic acidesters or (iii) vinyl acetate, such as acrylic rubbers; polyesterurethanes; ethylene-vinyl acetates; fluorinated rubbers;isoprene-acrylonitrile polymers; chlorosulfinated polyethylenes; andhomopolymers of polyvinyl acetate were found to be particularly useful.[See U.S. Pat. No. 4,440,910 to O'Connor, the disclosures of each ofwhich are hereby expressly incorporated herein by reference.] Theelastomeric polymers are described in the '910 patent as eitherhomopolymers of alkyl esters of acrylic acid; copolymers of anotherpolymerizable monomer, such as lower alkenes, with an alkyl or alkoxyester of acrylic acid; and copolymers of alkyl or alkoxy esters ofacrylic acid. Other unsaturated monomers which may be copolymerized withthe alkyl and alkoxy esters of acrylic include dienes, reactivehalogen-containing unsaturated compounds and other acrylic monomers suchas acrylamides.

For instance, one group of such elastomeric polymers are copolymers ofmethyl acrylate and ethylene, manufactured by DuPont, under the name ofVAMAC, such as VAMAC N123 and VAMAC B-124. VAMAC N123 and VAMAC B-124are reported by DuPont to be a master batch of ethylene/acrylicelastomer. The DuPont material VAMAC G is a similar copolymer, butcontains no fillers to provide color or stabilizers. VAMAC VCS rubberappears to be the base rubber, from which the remaining members of theVAMAC product line are compounded. VAMAC VCS (also known as VAMAC MR) isa reaction product of the combination of ethylene, methyl acrylate andmonomers having carboxylic acid cure sites, which once formed is thensubstantially free of processing aids (such as the release agentsoctadecyl amine, complex organic phosphate esters and/or stearic acid),and anti-oxidants (such as substituted diphenyl amine).

DuPont provides to the market under the trade designation VAMAC VMX 1012and VCD 6200, rubbers which are made from ethylene and methyl acrylate.It is believed that the VAMAC VMX 1012 rubber possesses little to nocarboxylic acid in the polymer backbone. Like the VAMAC VCS rubber, theVAMAC VMX 1012 and VCD 6200 rubbers are substantially free of processingaids such as the release agents octadecyl amine, complex organicphosphate esters and/or stearic acid, and anti-oxidants, such assubstituted diphenyl amine, noted above. All of these VAMAC elastomericpolymers are useful herein.

In addition, vinylidene chloride-acrylonitrile copolymers [see U.S. Pat.No. 4,102,945 (Gleave)] and vinyl chloride/vinyl acetate copolymers [seeU.S. Pat. No. 4,444,933 (Columbus)] may be included in the Part Acomposition. Of course, the disclosures of each these U.S. patents arehereby incorporated herein by reference in their entirety.

Copolymers of polyethylene and polyvinyl acetate, available commerciallyunder the trade name LEVAMELT by LANXESS Limited, are useful.

A range of LEVAMELT-branded copolymers are available and includes forexample, LEVAMELT 400, LEVAMELT 600 and LEVAMELT 900. The LEVAMELTproducts differ in the amount of vinyl acetate present. For example,LEVAMELT 400 comprises an ethylene-vinyl acetate copolymer comprising 40percent by weight vinyl acetate. The LEVAMELT products are supplied ingranular form. The granules are almost colourless and dusted with silicaand talc. LEVAMELT consists of methylene units forming a saturated mainchain with pendant acetate groups. The presence of a fully saturatedmain chain is an indication that LEVAMELT-branded copolymers areparticularly stable; they do not contain any reactive double bonds whichmake conventional rubbers prone to aging reactions, ozone and UV light.The saturated backbone is reported to make the polymer robust.

Interestingly, depending on the ratio of polyethylene/polyvinylacetate,the solubilities of these LEVAMELT-branded elastomers change indifferent monomers and also the ability to toughen changes as a resultof the solubility.

The LEVAMELT-branded elastomers are available in pellet form and areeasier to formulate than other known elastomeric toughening agents.

LEVAPREN-branded copolymers, also from Lanxess, may also be used.

VINNOL-branded surface coating resins available commercially from WackerChemie AG, Munich, Germany represent a broad range of vinylchloride-derived copolymers and terpolymers that are promoted for use indifferent industrial applications. The main constituents of thesepolymers are different compositions of vinyl chloride and vinyl acetate.The terpolymers of the VINNOL product line additionally contain carboxylor hydroxyl groups. These vinyl chloride/vinyl acetate copolymers andterpolymers may also be used.

VINNOL-branded surface coating resins with carboxyl groups areterpolymers of vinyl chloride, vinyl acetate and dicarboxylic acids,varying in terms of their molar composition and degree and process ofpolymerization. These terpolymers are reported to show excellentadhesion, particularly on metallic substrates.

VINNOL-branded surface coating resins with hydroxyl groups arecopolymers and terpolymers of vinyl chloride, hydroxyacrylate anddicarboxylate, varying in terms of their composition and degree ofpolymerization.

VINNOL-branded surface coating resins without functional groups arecopolymers of vinyl chloride and vinyl acetate of variable molarcomposition and degree of polymerization.

Rubber particles, especially rubber particles that have relatively smallaverage particle size (e.g., less than about 500 nm or less than about200 nm), may also be included, particularly in the Part B composition.The rubber particles may or may not have a shell common to knowncore-shell structures.

In the case of rubber particles having a core-shell structure, suchparticles generally have a core comprised of a polymeric material havingelastomeric or rubbery properties (i.e., a glass transition temperatureless than about 0° C., e.g., less than about −30° C.) surrounded by ashell comprised of a non-elastomeric polymeric material (i.e., athermoplastic or thermoset/crosslinked polymer having a glass transitiontemperature greater than ambient temperatures, e.g., greater than about50° C.). For example, the core may be comprised of a diene homopolymeror copolymer (for example, a homopolymer of butadiene or isoprene, acopolymer of butadiene or isoprene with one or more ethylenicallyunsaturated monomers such as vinyl aromatic monomers,(meth)acrylonitrile, (meth)acrylates, or the like) while the shell maybe comprised of a polymer or copolymer of one or more monomers such as(meth)acrylates (e.g., methyl methacrylate), vinyl aromatic monomers(e.g., styrene), vinyl cyanides (e.g., acrylonitrile), unsaturated acidsand anhydrides (e.g., acrylic acid), (meth)acrylamides, and the likehaving a suitably high glass transition temperature. Other rubberypolymers may also be suitably be used for the core, includingpolybutylacrylate or polysiloxane elastomer (e.g., polydimethylsiloxane,particularly crosslinked polydimethylsiloxane).

Typically, the core will comprise from about 50 to about 95 percent byweight of the rubber particles while the shell will comprise from about5 to about 50 percent by weight of the rubber particles.

Preferably, the rubber particles are relatively small in size. Forexample, the average particle size may be from about 0.03 to about 2microns or from about 0.05 to about 1 micron. The rubber particles mayhave an average diameter of less than about 500 nm, such as less thanabout 200 nm. For example, the core-shell rubber particles may have anaverage diameter within the range of from about 25 to about 200 nm.

When used, these core shell rubbers allow for toughening to occur in thecomposition and oftentimes in a predictable manner—in terms oftemperature neutrality toward cure—because of the substantial uniformdispersion, which is ordinarily observed in the core shell rubbers asthey are offered for sale commercially.

In the case of those rubber particles that do not have such a shell, therubber particles may be based on the core of such structures.

Desirably, the rubber particles are relatively small in size. Forexample, the average particle size may be from about 0.03 to about 2μ orfrom about 0.05 to about 1μ. In certain embodiments of the invention,the rubber particles have an average diameter of less than about 500 nm.In other embodiments, the average particle size is less than about 200nm. For example, the rubber particles may have an average diameterwithin the range of from about 25 to about 200 nm or from about 50 toabout 150 nm.

The rubber particles may be used in a dry form or may be dispersed in amatrix, as noted above.

Typically, the composition may contain rubber particles in an amountfrom about 5 to about 35 percent by weight.

Combinations of different rubber particles may advantageously be used inthe present invention. The rubber particles may differ, for example, inparticle size, the glass transition temperatures of their respectivematerials, whether, to what extent and by what the materials arefunctionalized, and whether and how their surfaces are treated.

Rubber particles that are suitable for use in the present invention areavailable from commercial sources. For example, rubber particlessupplied by Eliokem, Inc. may be used, such as NEP R0401 and NEP R401S(both based on acrylonitrile/butadiene copolymer); NEP R0501 (based oncarboxylated acrylonitrile/butadiene copolymer; CAS No. 9010-81-5); NEPR0601A (based on hydroxy-terminated polydimethylsiloxane; CAS No.70131-67-8); and NEP R0701 and NEP 0701S (based onbutadiene/styrene/2-vinylpyridine copolymer; CAS No. 25053-48-9). Also,those available under the PARALOID tradename, such as PARALOID 2314,PARALOID 2300, and PARALOID 2600, from Dow Chemical Co., Philadelphia,Pa., and those available under the STAPHYLOID tradename, such asSTAPHYLOID AC-3832, from Ganz Chemical Co., Ltd., Osaka, Japan.

Rubber particles that have been treated with a reactive gas or otherreagent to modify the outer surfaces of the particles by, for instance,creating polar groups (e.g., hydroxyl groups, carboxylic acid groups) onthe particle surface, are also suitable for use herein. Illustrativereactive gases include, for example, ozone, Cl₂, F₂, O₂, SO₃, andoxidative gases. Methods of surface modifying rubber particles usingsuch reagents are known in the art and are described, for example, inU.S. Pat. Nos. 5,382,635; 5,506,283; 5,693,714; and 5,969,053, each ofwhich being hereby expressly incorporated herein by reference in itsentirety. Suitable surface modified rubber particles are also availablefrom commercial sources, such as the rubbers sold under the tradenameVISTAMER by Exousia Corporation.

Where the rubber particles are initially provided in dry form, it may beadvantageous to ensure that such particles are well dispersed in theadhesive composition prior to curing the adhesive composition. That is,agglomerates of the rubber particles are preferably broken up so as toprovide discrete individual rubber particles, which may be accomplishedby intimate and thorough mixing of the dry rubber particles with othercomponents of the adhesive composition.

Thickeners are also useful.

Stabilizers and inhibitors may also be employed to control and preventpremature peroxide decomposition and polymerization. The inhibitors maybe selected from hydroquinones, benzoquinones, naphthoquinones,phenanthroquinones, anthraquinones, and substituted compounds thereof.Various phenols may also be used as inhibitors, such as2,6-di-tertiary-butyl-4-methyl phenol. The inhibitors may be used inquantities of about 0.1% to about 1.0% by weight of the totalcomposition without adverse effect on the curing rate of thepolymerizable adhesive composition.

Tougheners may be used in the Part B composition. Those contemplated foruse in the Part B composition include a (meth)acrylate-functionalizedurethane resin having a backbone, at least a portion of which includes aurethane linkage formed from isophorane diisocyanate. An example of the(meth)acrylate-functionalized urethane resin is a urethane(meth)acrylate resin made from an alkylane glycol (such as polypropyleneglycol), isophorane diisocyanate and hydroxy alkyl(meth)acrylate (suchas hydroxyl ethyl acrylate). Other examples include a polyester ofhexanedioic acid, diethylene glycol, terminated with isophoronediisocyanate, capped with 2-hydroxyethyl acrylate; a polytetramethyleneglycol ether terminated with isophorone diisocyanate, capped with2-hydroxyethyl methacrylate; and a hydroxy terminated polybutadieneterminated with isophorone diisocyanate, capped with 2-hydroxyethylacrylate.

Alkyl (meth)acrylates useful in making the (meth)acrylate-functionalizedurethane resin includes isobornyl(meth)acrylate, isodecyl(meth)acrylate,lauryl(meth)acrylate, cyclic trimethylolpropane formal acrylate,octyldecyl acrylate, tetrahydrofurfuryl(meth)acrylate,tridecyl(meth)acrylate, and hydroxypropyl(meth)acrylate, among others.

Hydroxy alkyl(meth)acrylates include 2-hydroxyethyl(meth)acrylate,phenoxyethyl(meth)acrylate, N-vinyl caprolactam, N,N-dimethylacrylamide, 2(2-ethoxyethoxy) ethyl acrylate, caprolactone acrylate,polypropylene glycol monomethacrylate, 1,3-butylene glycoldimethacrylate, 1,4-butanediol dimethacrylate, 1,6 hexanedioldi(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate,tripropylene glycol diacrylate, ethoxylated trimethylolpropanetriacrylate, trimethylolpropane triacrylate, tris(2-hydroxy ethyl)isocyanurate triacrylate, and combinations thereof.

Instead of hydroxy ethyl(meth)acrylate, 1,4-butanediol dimethacrylate,1,6 hexanediol di(meth)acrylate, tricyclodecane dimethanoldi(meth)acrylate, tripropylene glycol diacrylate, ethoxylatedtrimethylolpropane triacrylate, trimethylolpropane triacrylate, andtris(2-hydroxy ethyl) isocyanurate triacrylate may be used to cap theso-formed urethane (meth)acrylate resin.

In one aspect of the invention, reaction products of the compositiondemonstrate a greater drop impact strength on substrates bonded togetherin a 1 mm spaced apart relationship than on substrates bonded togetherin a 0 mm spaced apart relationship.

In practice, each of the Part A and the Part B compositions are housedin separate containment vessels in a device prior to use, where in usethe two parts are expressed from the vessels mixed and applied onto asubstrate surface. The vessels may be chambers of a dual chamberedcartridge, where the separate parts are advanced through the chamberswith plungers through an orifice (which may be a common one or adjacentones) and then through a mixing dispense nozzle. Or the vessels may becoaxial or side-by-side pouches, which may be cut or torn and thecontents thereof mixed and applied onto a substrate surface.

The invention will be more readily appreciated by a review of theexamples, which follow.

Examples

Reference to CA or cyanoacrylate in the Examples refers to ECA orethyl-2-cyanoacrylate, respectively, unless otherwise noted.

With reference to Table 1, an adhesive system was prepared for controlpurposes where the Part A included ECA, mixed with LEVAPREN 900, t-BPBand a boron trifluoride/methane sulfonic acid combination, and the PartB included as the (meth)acrylate component the combination of anacrylated urethane ester, HPMA, and CN 2003 EU, to which was added ahydrated copper chlorate and a filler package as noted.

TABLE 1 Part A Components Sample/Amt (grams) Type Identity A1Cyanoacrylate ECA 68.9 Toughener LEVAPREN 900* 22.5 Peroxide t-BPB 5.0Stabilizer⁺ BF₃/MSA 7.6 Part B Components Sample/Amt (grams) TypeIdentity B1 (Meth)acrylate Acrylated 42.23 Urethane Ester¹ HPMA 25 CN2003 EU² 22.5 Transition Metal Cu (ClO₄)₂ · (H₂O)₆ 5 Filler CAB-O-SIL TS720 9 HOMBINAN LW 7.5 *Ethylene/vinyl acetate copolymer, availablecommercially from Lanxess Ltd. +As a stock solution ¹made in sequentialsteps from the reaction of diols and dicarboxylic acids to formpolyester diols, followed by reaction with toluene diisocyanate andfinally capping with hydroxy propyl (meth) acrylate ²Epoxy acrylate, asreported by the manufacturer, Sartomer division of Arkema

For reference, the A1-B1 system from Table 1 showed drop impact strengthperformance of 6.3 Joules at 0 mm gap and 1.59 Joules at 1 mm gap, basedon an average of six replicates.

Here, the Part B composition from Table 1 was used in an amount of 70percent by weight with 30 percent by weight of a variety of(meth)acrylate-functionalized compounds, most of which having a Tg ofless than about −5° C., and one not. These Part B compositions are notedin Table 2 below as B2, B3, B4, B5, B6 and B7, respectively, and areused together with the Part A composition from Table 1, namely A1.

TABLE 2 Components Sample/Amt (weight percent) Type Identity B2 B3 B4 B5B6 B7 (meth)acrylate- SR-256 30 functionalized PPG Diacrylate 30compound CD-9075 30 SR-335 30 SR-278 30 SR-339 30

The A1-B2, A1-B3, A1-B4, A1-B5 and A1-B6 systems were mixed anddispensed onto grit blasted mild steel lap shears in a 0 mm gapconfiguration and a 1 mm gap configuration with the noted substratemated in an overlapped, off-set manner with the adhesive system disposedbetween the substrates in the overlapped, off-set portion.

In Table 3 below, the drop impact strength of these systems is recorded.

TABLE 3 Drop Impact Strength, Joules Sample 0 mm 1 mm A1-B2 2.8 6.0A1-B3 2.9 19.2 A1-B4 5.9 15.0 A1-B5 4.8 1.4 A1-B6 4.4 10.4 A1-B7 7.011.7

At 0 mm gap, the A1-B2, A1-B3, A1-B4, A1-B6 and A1-B7 systems showeddrop impact strength of 2.8, 2.9, 5.9, 4.4 and 7.0 Joules, respectively.At 1 mm gap, the A1-B2, A1-B3, A1-B4, A1-B6 and A1-B7 systems showeddrop impact strength of 6.0, 19.2, 15.0, 10.4 and 11.7 Joules,respectively. (See FIGS. 1-2.)

Compared to the performance shown in the A1-B1 system, the A1-B4 andA1-B7 systems showed comparable performance at 0 mm. However, at 1 mmgap, the A1-B1 system showed drop impact strength performance of 1.6Joules, whereas all of the systems but A1-B5 shown in Table 2 havebetter performance than that. And the A1-B2 and A1-B6 systems showedimproved drop impact strength performance in the 1 mm gap configurationof nearly two times over the 0 mm gap configuration, the A1-B4 systemshowed improved drop impact strength performance in the 1 mm gapconfiguration of nearly three times over the 0 mm gap configuration, andthe A1-B3 system showed improved drop impact strength performance in the1 mm gap configuration of nearly nine times over the 0 mm gapconfiguration, all of which was quite unexpected. (See FIGS. 1-2.)

What is claimed is:
 1. A two-part curable composition comprising: (a) a first part comprising a cyanoacrylate component and a peroxide catalyst; and (b) a second part comprising a free radical curable component and a transition metal, wherein at least one of the first part or the second part further comprises a (meth)acrylate-functionalized compound having a Tg of less than 0, and wherein when mixed together the peroxide catalyst initiates cure of the free radical curable component and the transition metal initiates cure of the cyanoacrylate component.
 2. The composition of claim 1, wherein the cyanoacrylate component comprises H₂C═C(CN)—COOR, wherein R is selected from alkyl, alkoxyalkyl, cycloalkyl, alkenyl, aralkyl, aryl, allyl and haloalkyl groups.
 3. The composition of claim 1, wherein the peroxide catalyst comprises perbenzoates.
 4. The composition of claim 1, wherein the peroxide catalyst is t-butyl perbenzoate.
 5. The composition of claim 1, wherein the (meth)acrylate-functionalized compound is present in the second part.
 6. The composition of claim 1, wherein the peroxide catalyst is present in an amount from about 0.01 percent to about 10 percent by weight, based on the cyanoacrylate component.
 7. The composition of claim 1, wherein the free radical curable component is a (meth)acrylate component selected from the group consisting of polyethylene glycol di(meth)acrylates, tetrahydrofuran (meth)acrylates and di(meth)acrylates, hydroxypropyl (meth)acrylate, hexanediol di(meth)acrylate, trimethylol propane tri(meth)acrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, benzylmethacrylate, tetraethylene glycol dimethacrylate, dipropylene glycol dimethacrylate, di-(pentamethylene glycol) dimethacrylate, tetraethylene diglycol diacrylate, diglycerol tetramethacrylate, tetramethylene dimethacrylate, ethylene dimethacrylate, neopentyl glycol diacrylate, trimethylol propane triacrylate, ethoxylated bisphenol-A (meth)acrylate, ethoxylated bisphenol-F (meth)acrylate, and methacrylate-functional urethanes.
 8. The composition of claim 1, wherein the transition metal comprises a member selected from the group consisting of copper, vanadium, cobalt and iron.
 9. The composition of claim 1, wherein the first part is housed in a first chamber of a dual chamber syringe and the second part is housed in a second chamber of the dual chamber syringe.
 10. The composition of claim 1, wherein the second part further comprises at least one of a plasticizer and a filler.
 11. The composition of claim 1, wherein the first part further comprises a toughener.
 12. The composition of claim 11, wherein the toughener is a member selected from the group consisting of (a) reaction products of the combination of ethylene, methyl acrylate and monomers having carboxylic acid cure sites, (b) dipolymers of ethylene and methyl acrylate, (c) combinations of (a) and (b), (4) vinylidene chloride-acrylonitrile copolymers, (5) and vinyl chloride/vinyl acetate copolymer, (6) copolymers of polyethylene and polyvinyl acetate, and combinations thereof.
 13. The composition of claim 1, wherein when disposed between two substrates spaced apart by about 1 mm, reaction products thereof demonstrate a drop impact strength of about 5 Joules or greater.
 14. The composition of claim 1, wherein the (meth)acrylate-functionalized compound has a Tg within the range of about 0 to about −120° C.
 15. The composition of claim 1, wherein the (meth)acrylate-functionalized compound is present in an amount of about 15 to about 50 percent by weight of the free radical curable component of the Part B composition.
 16. The composition of claim 1, wherein cured reaction products of the composition demonstrate a greater drop impact strength on substrates bonded together in a 1 mm spaced apart relationship than on substrates bonded together in a 0 mm spaced apart relationship. 